2,6-Dihydroxynaphthalene (to be referred to sometimes as 2,6-DHN hereinafter) can be obtained by oxidizing 2,6-diisopropylnaphthalene (to be referred to sometimes as 2,6-DIPN hereinafter) to form 2,6-diisopropylnaphthalene dihydroperoxide (to be referred to sometimes as DHP hereinafter) and acid-cleaving the product in the presence of an oxidation catalyst. 2,6-Diisopropylnaphthalene is useful as a raw material for synthetic resins, synthetic fibers, medicines, agricultural chemicals, dyes, etc.
A batchwise process for oxidizing p-diisopropylbenzene, different from 2,6-diisopropylnaphthalene, has previously been known which comprises oxidizing p-diisopropylbenzene with molecular oxygen at a temperature of 80.degree. to 120.degree. C. until the concentration of hydroperoxide calculated as p-diisopropylbenzene monohydroperoxide in the oxidation reaction product becomes at least 115% by weight while optionally feeding an aqueous alkaline solution having a pH higher than 10 so as to maintain the pH of the oil layer in the reaction system at 9 to 11 during the reaction and while on the other hand, optionally removing the aqueous layer from the reaction system so as to maintain the amount of water in the reaction system at 5 to 60% by weight (see Japanese Patent Publication No. 44066/1980 and Japanese Laid-Open Patent Publication No. 72144/1973).
In the aforesaid oxidation of p-diisopropylbenzene, the amount of water in the aqueous layer of the reaction system is adjusted to 5 to 60% by weight while the pH of the oil layer is maintained at 9 to 11 during the reaction.
Japanese Laid-Open Patent Publication No. 34,138/1976 discloses a process which comprises bringing beta-isopropylnaphthalene into intimate contact with molecular oxygen in an aqueous alkaline medium with stirring at about 75.degree. to 100.degree. C. in the presence of 25 to 1,000 ppm, based on beta-isopropylnaphthalene, of a specific nickel (II), rhodium (I) or Ir compound (catalyst); separating the reaction mixture into an aqueous layer and an oily layer; and recovering beta-isopropylnaphthalene hydroperoxide from the oily layer.
Likewise, British Patent Specification No. 654,035 discloses a process for producing beta-isopropylnaphthalene hydroxide, which comprises reacting beta-isopropylnaphthalene with molecular oxygen in the liquid phase at an elevated temperature in the substantial absence of a heavy metal oxidation catalyst.
The processes described in the above-cited Japanese Laid-Open Patent Publication No. 34,138/1976 and British Pat. No. 654,035 are for the oxidation of monoisopropylnaphthalene and not for the oxidation of diisopropylnaphthalene.
U.S. Pat. No. 4,503,262 discloses a process for converting 2,6-diisopropylnaphthalene to 2,6-diisopropylnaphthalene hydroperoxide, which comprises dissolving the 2,6-diisopropylnaphthalene in a C.sub.5-14 aliphatic hydrocarbon and bringing the solution into contact with an oxygen-containing gas in a basic medium at an elevated temperature in the range of about 50.degree. C. to about 100.degree. C. under atmospheric pressure in the presence of a catalyst selected from the group consisting of oxides, hydroxides and organic acid salts of heavy metals, and mixtures thereof.
U.S. Pat. No. 4,503,262 discloses that the process described there has the advantage of increasing the rate of the reaction and improving the yield and purity of hydroperoxide.
It is an object of this invention to provide a process for oxidizing 2,6-diisopropylnaphthalene with molecular oxygen.
Another object of this invention is to provide a process which comprises oxidizing 2,6-diisopropylnaphthalene with molecular oxygen to form an oxidation product composed mainly of 2,6-diisopropylnaphthalene dihydroperoxide, monohydroxymonoperoxide and dihydroxide in a high conversion from 2,6-diisopropylnaphthalene.
Still another object of this invention is to provide a process for producing 2,6-dihydroxynaphthalene in a high yield which comprises subjecting the oxidation product obtained by the above oxidation process of the invention to oxidation and acid cleavage using hydrogen peroxide.
Yet another object of this invention is to provide a process in which purified 2,6-dihydroxynaphthalene is recovered in a high yield from the reaction mixture containing 2,6-dihydroxynaphthalene obtained by the above oxidation and acid cleavage.
A further object of this invention is to provide a process for producing 2,6-diacetoxynaphthalene, which comprises converting 2,6-dihydroxynaphthalene obtained by the above oxidation and acid cleavage into 2,6-diacetoxynaphthalene and recovering it.
Additional objects and advantages of this invention will become apparent from the following description.